In contemporary optical-electronic hybrid systems, an optical fiber interfaces with an opto-electronic device. The opto-electronic device typically includes a hermetic package, having a plurality of conductive leads for electronic communication with devices external to the package.
During manufacture, single or multiple fiber optic pigtails are inserted through ferrules provided in side walls of the package. The end face of each pigtail is typically positioned and bonded to a bench or submount installed within the package. The body of each pigtail is bonded to a corresponding ferrule to facilitate the hermetic seal of the package.
As opto-electronic technology continues to evolve, there is a continuous drive toward higher integration. This generally requires an increased number of fiber pigtails to extend across the package perimeter, as well as an increased need for heightened precision in aligning the fiber endfaces with internal opto-electronic components.
A standard fiber optic cross section is illustrated in FIG. 1. A fiber core 12 is encased in cladding 14. The fiber core may for example be comprised of silica, while the cladding may be comprised of silica having a lower index of refraction than that of the core 12. The cladding 14 is encased in a coating 16 which is, in turn, surrounded by a protective jacket 18. The coating and protective jacket may, for example, be formed of any of a number of polymers. In a popular configuration, the diameters of the core 12, cladding 14, coating 16, and protective jacket 18 layers are 9 xcexcm, 125 xcexcm, 250 xcexcm, and 900-3000 xcexcm, respectively.
Despite precision processing during manufacture of optical fibers, a number of variations in the finished fiber can occur. These include variation in the cladding 14 diameter, and variation in the center position of the core 12 relative to the center of the cladding 14, i.e., core-cladding eccentricity.
With reference to the end view of FIG. 2, in order to manage fiber congestion in a device, the fibers are commonly arranged into an array on a silicon bench. The bench 22 includes an upper bench portion 22A and a lower bench portion 22B. A number of opposed V-grooves 28A, 28B are formed in the upper and lower bench portions 22A, 22B. The V-grooves are formed in parallel with respect to each other, and at precise intervals which, for example, may be periodic.
The outer protective jacket 18 and coating 16 are stripped from the fiber ends, and the ends are positioned and bonded between the V-grooves 28A, 28B. When the fibers are bonded, the aforementioned variations can result in misalignment of the fiber cores with the intended interface, for example the optical components that are installed in the submount. With reference to the example provided in FIG. 2, the respective cladding diameters of fibers 20A, 20B, and 20C are consistent, and therefore their respective fiber center positions 24A, 24B, 24C are properly centered with respect to the upper and lower V-grooves 28A, 28B. However, the cladding diameters of fibers 20D and 20E are smaller than those of fibers 20A, 20B, and 20C, and therefore their respective fiber center positions 24D, 24E are not centered between the upper and lower V-grooves 28A, 28B. This variation in cladding outer diameter causes a height offset between the respective fibers in the array.
Ideally, the fiber core 26D is located directly at the fiber center position 24D, as shown in fiber 20D. However, due to manufacturing imprecision, the fiber core 26A, 26B, 26C, 26E can vary in radial distance from the fiber center position 24A, 24B, 24C, 24E as shown in fibers 20A, 20B, 20C, and 20E, i.e., core eccentricity. As a result, the position and angular orientation of the fiber core 26 can vary with respect to the center position of the upper and lower V-grooves 28A, 28B, as shown. Such a variance can also cause a height offset, as well as angular offset, between beams emitted from the respective fibers, or the input apertures that define where a beam must be focused to be coupled into, and be propagated by, the fiber.
The present invention is directed to an apparatus and method that addresses the limitations of conventional approaches described above. Particularly, the present invention provides an apparatus and method by which height offset and/or angular core offset of optical fibers that are mounted in an array are mitigated. In this manner, a level of precision is achieved that is advantageous for application in opto-electronic systems.
The fibers are preferably mounted in the array such that the respective core-to-clad offset axes of the fibers, defined between the fiber core center and the cladding center of each fiber, are at substantially the same angle with respect to the lateral axis of the bench The fiber pigtails are preferably cut from the same fiber spool, ensuring consistency in cladding outer diameter. In this manner, precision in core-to-core pitch and consistency in core-to-core height are achieved in the fiber array.
In one aspect, the present invention is directed to a fiber array. The array includes a bench and fiber pigtails. The bench includes seats for receiving the fiber pigtails. The fibers are mounted in the seats; the fibers include a fiber core and cladding surrounding the fiber core. Each fiber has a core-to-clad offset axis defined between the fiber core center and the cladding center of each fiber. This is a measure of the core eccentricity. The fibers are mounted in the array such that the respective core-to-clad offset axes of the fibers are at substantially the same angle with respect to each other.
In another aspect, the present invention is directed to a fiber array including a bench and fiber pigtails. The bench includes a plurality of parallel seats for receiving the fibers. Fibers are mounted in the seats. The fibers comprise a fiber core and cladding surrounding the fiber core, and are cut from a common fiber spool. The angle between the core-to-clad offset axes and a plane of the submount may be 90 degrees, 0 degrees, or an acute angle.
In preferred embodiments, the seats comprise V-grooves, and the bench comprises silicon. The bench includes an upper portion and a lower portion; the upper and lower portions each include opposed seats for housing inserted fibers. Alternatively, the bench includes an upper portion and a lower portion, wherein the lower portion includes the seats and wherein the upper portion comprises a plate.
In another aspect, the present invention is directed to a method of forming a fiber array. A bench is provided, the bench including a plurality of parallel seats for receiving a plurality of fibers. Fibers are mounted in the seats, the fibers comprising a fiber core and cladding surrounding the fiber core, each fiber having a core-to-clad offset axis defined between the fiber core center and the cladding center of each fiber. The fibers are mounted in the array such that the respective core-to-clad offset axes of the fibers are substantially parallel to each other.
In yet another aspect, the present invention is directed to a method of forming a fiber array. A bench is provided, the bench including a plurality of parallel seats for receiving a plurality of fibers. A plurality of fibers are mounted in the seats, the fibers comprising a fiber core and cladding surrounding the fiber core, the fibers being cut from a common fiber spool.
In another aspect, the present invention is directed to a method for aligning fibers in a fiber array with an optical component on a substrate. Fibers are mounted and rotationally oriented in a fiber bench in response to a direction of core-to-cladding offset axes of the fibers. The fiber bench is in turn mounted to a substrate in alignment with a component mounted to the substrate, such that the fibers are aligned with the component.